Submitted to: Peanut Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/10/2008
Publication Date: 11/25/2008
Citation: Dorner, J.W. 2008. Relationship Between Kernel Moisture Content and Water Activity in Different Maturity Stages of Peanut. 2008. Peanut Science. v 35 pp 77-80. Interpretive Summary: Aflatoxin contamination of peanuts, which is caused by the molds, Aspergillus flavus and A. parasiticus, is an issue that must be dealt with to ensure the safety of peanuts for human consumption. Ensuring that safety is a major concern for the peanut industry that is also very costly. Much research has been and continues to be conducted to alleviate the problem. Preharvest aflatoxin contamination occurs when peanuts are subjected to late-season drought conditions, and two major factors in contamination are peanut kernel water activity and pod maturity. Water activity is a measure of the water in the kernel that is actually available to support fungal growth, and the aflatoxin-producing fungi require specific water activities to grow and produce aflatoxin. Immature peanuts are more susceptible to preharvest aflatoxin contamination than mature ones. Because most determinations of peanut kernel moisture measure the total moisture content, this study was undertaken to determine the relationship between total kernel moisture content and water activity using kernels from different maturity stages. Results showed large differences in total moisture content at specific water activities for different maturity stages. For example, at an optimal water activity for aflatoxin production of 0.95, the moisture content for very immature peanuts was found to be as high as 45% while in mature peanuts total moisture was about 20%. Equations were developed so that water activity could be predicted from measurements of total kernel moisture in five different maturity stages of peanut. This information can lead to better understanding of the process of preharvest aflatoxin contamination and assist breeding programs with the goal of developing peanuts that are more resistant to contamination.
Technical Abstract: The water activity (aw) and moisture content (KMC) of individual peanut kernels representing five different maturity stages were measured during a period of late-season drought stress leading up to normal harvest time. Curves were generated describing the relationship between aw and KMC for yellow 1, yellow 2, orange, brown, and black maturity stages as determined by the peanut hull scrape method. As peanuts matured, the KMC for a given aw decreased. KMC in the most immature yellow 1 stage was extremely variable at higher aw levels, indicative of the rapidly changing composition of kernels at that stage. The variation in KMC at high aw decreased with increasing maturity. Equations to predict KMC for given aw showed that KMC varied greatly among maturity stages, particularly at higher aw. For example, at an aw of 0.99 the predicted KMCs for yellow 1(least mature) and black (most mature) stages were 62.7 and 30.7%, respectively. The degree of variation among stages decreased as aw decreased in response to drought stress. Because preharvest aflatoxin contamination of peanuts is highly dependent on both the maturity stage of peanuts during periods of late-season drought stress and the resulting aw of kernels, these KMC-aw relationships can be utilized in efforts to breed peanuts for reduced susceptibility to aflatoxin contamination.